National polls put Barack Obama in the mid-40s and slightly underwater, which could indicate trouble for him in 2012 — if the Presidency was won on a national popular vote.  (Ask Al Gore how that works out.)  National Journal took a look at polling in battleground states and sees a much bigger problem than national polls indicate:

In every reputable battleground state poll conducted over the past month, Obama’s support is weak. In most of them, he trails Republican front-runner Mitt Romney.  For all the talk of a closely fought 2012 election, if Obama can’t turn around his fortunes in states such as Michigan and New Hampshire, next year’s presidential election could end up being a GOP landslide.

Take Ohio, a perennial battleground in which Obama has campaigned more than in any other state (outside of the D.C. metropolitan region). Fifty percent of Ohio voters now disapprove of his job performance, compared with 46 percent who approve, according to a Quinnipiac pollconducted from July 12-18.

Among Buckeye State independents, only 40 percent believe that Obama should be reelected, and 42 percent approve of his job performance. Against Romney, Obama leads 45 percent to 41 percent—well below the 50 percent comfort zone for an incumbent.

The news gets worse from there.  In Michigan, a reliably Democratic state that Obama carried with 57 percent of the vote, an EPIC-MRA pollconducted July 9-11 finds him trailing Romney, 46 percent to 42 percent. Only 39 percent of respondents grade his job performance as “excellent” or good,” with 60 percent saying it is “fair” or “poor.” The state has an unemployment rate well above the national average, and the president’s approval has suffered as a result.

Obama also trails Romney in New Hampshire, getting edged by two points.  More worrisome for the White House is Obama’s standing in these states, and others like them.  Regardless of who the nominee is, having re-elect numbers in the low 40s is a clear sign that the state is up for grabs. And it’s not just these states, either.

If Michigan is in play — and it almost certainly will be — then Pennsylvania and Wisconsin probably are as well, and Indiana may already be lost.  That Rust Belt band played heavily into Obama’s victory in 2008.  Hillary Clinton Democrats, primarily white working-class voters, turned out for Obama in 2008, but those are the voters Obama is losing fastest in this cycle.  National Journal wonders whether Obama can hold Colorado, Nevada, and Virginia, but they miss North Carolina, where Obama’s standing has already shown to be crumbling, too.

Most presidential re-election runs have some element of defense to hold territory won in the previous election, but that may be the only strategy Obama can put in play.  Obama won the Electoral College handily in 2008, 365-173.  By flipping Pennsylvania, Ohio, Florida, Indiana, Colorado, Virginia, Nevada, and Wisconsin, Republicans edge Obama 295-243.  Swapping Florida for North Carolina still produces a 281-257 win for Republicans.  Winning Michigan and conceding Colorado makes it 288-250 Republicans.

You can bet that the Obama campaign is studying the map very, very carefully in order to see where they want to spend money, and it’s mostly going to go in that Rust Belt area.  Republicans should plan accordingly.  That could be the key to the entire election.